annotate @ 48:40caeb9e9b25

switched to new header macro; cleaned up CW
date Mon, 12 Apr 2010 14:45:29 +0200
parents b6ae4a8ab1d3
children 2f188a5dc0dc
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meillo@36 1 .nr PS 11
meillo@36 2 .nr VS 13
meillo@47 3
meillo@0 4 .de CW
meillo@0 5 .nr PQ \\n(.f
meillo@48 6 .if t \{\
meillo@48 7 . ft CW
meillo@48 8 . if !^\\$1^^ \&\\$1\f\\n(PQ\\$2
meillo@48 9 .\}
meillo@48 10 .if n \{\
meillo@48 11 . ie ^\\$1^^ .ul 999
meillo@48 12 . el .ul 1
meillo@48 13 . if \\n(.$=1 \&\\$1
meillo@48 14 . if \\n(.$>1 \&\\$1\c
meillo@48 15 . if \\n(.$>1 \&\\$2
meillo@48 16 .\}
meillo@0 17 ..
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meillo@0 19 .ds [. \ [
meillo@0 20 .ds .] ]
meillo@42 21
meillo@48 22 .de H
meillo@48 23 .if '\\$1'1' \{\
meillo@48 24 . sp 2v
meillo@48 25 . nr PS +2
meillo@48 26 . NH \\$1
meillo@48 27 \\$2
meillo@48 28 . nr PS -2
meillo@48 29 . LP
meillo@48 30 . XS
meillo@48 31 . sp .5v
meillo@48 32 . B
meillo@48 33 \\*(SN \\$2
meillo@48 34 . XE
meillo@48 35 .\}
meillo@48 36 .if '\\$1'2' \{\
meillo@48 37 . NH \\$1
meillo@48 38 \\$2
meillo@48 39 . LP
meillo@48 40 . XS
meillo@48 41 \\*(SN \\$2
meillo@48 42 . XE
meillo@48 43 .\}
meillo@42 44 ..
meillo@42 45
meillo@45 46 .am QP
meillo@45 47 .ps -1
meillo@45 48 ..
meillo@45 49
meillo@47 50 .am DS
meillo@47 51 .CW
meillo@47 52 .ps -1
meillo@47 53 ..
meillo@47 54
meillo@1 55 .\"----------------------------------------
meillo@42 56
meillo@0 57 .TL
meillo@42 58 .ps +4
meillo@6 59 Why the Unix Philosophy still matters
meillo@0 60 .AU
meillo@0 61 markus schnalke <>
meillo@0 62 .AB
meillo@1 63 .ti \n(.iu
meillo@39 64 This paper explains the importance of the Unix Philosophy for software design.
meillo@0 65 Today, few software designers are aware of these concepts,
meillo@39 66 and thus a lot of modern software is more limited than necessary
meillo@39 67 and makes less use of software leverage than possible.
meillo@38 68 Knowing and following the guidelines of the Unix Philosophy makes software more valuable.
meillo@0 69 .AE
meillo@0 70
meillo@2 71 .FS
meillo@2 72 .ps -1
meillo@39 73 This paper was prepared for the ``Software Analysis'' seminar at University Ulm.
meillo@47 74 Mentor was professor Franz Schweiggert.
meillo@47 75 Handed in on 2010-04-12.
meillo@39 76 You may retrieve this document from
meillo@39 77 .CW \s-1 \ .
meillo@2 78 .FE
meillo@2 79
meillo@48 80 .H 1 Introduction
meillo@0 81 .LP
meillo@40 82 The Unix Philosophy is the essence of how the Unix operating system,
meillo@40 83 especially its toolchest, was designed.
meillo@40 84 It is no limited set of fixed rules,
meillo@40 85 but a loose set of guidelines which tell how to write software that
meillo@40 86 suites well into Unix.
meillo@40 87 Actually, the Unix Philosophy describes what is common to typical Unix software.
meillo@40 88 The Wikipedia has an accurate definition:
meillo@40 89 .[
meillo@44 90 wikipedia
meillo@44 91 unix philosophy
meillo@40 92 .]
meillo@40 93 .QP
meillo@40 94 The \fIUnix philosophy\fP is a set of cultural norms and philosophical
meillo@40 95 approaches to developing software based on the experience of leading
meillo@40 96 developers of the Unix operating system.
meillo@1 97 .PP
meillo@40 98 As there is no single definition of the Unix Philosophy,
meillo@40 99 several people have stated their view on what it comprises.
meillo@1 100 Best known are:
meillo@1 101 .IP \(bu
meillo@1 102 Doug McIlroy's summary: ``Write programs that do one thing and do it well.''
meillo@1 103 .[
meillo@44 104 mahoney
meillo@44 105 oral history
meillo@1 106 .]
meillo@1 107 .IP \(bu
meillo@1 108 Mike Gancarz' book ``The UNIX Philosophy''.
meillo@1 109 .[
meillo@44 110 gancarz
meillo@44 111 unix philosophy
meillo@1 112 .]
meillo@1 113 .IP \(bu
meillo@1 114 Eric S. Raymond's book ``The Art of UNIX Programming''.
meillo@1 115 .[
meillo@44 116 raymond
meillo@44 117 art of unix programming
meillo@1 118 .]
meillo@0 119 .LP
meillo@1 120 These different views on the Unix Philosophy have much in common.
meillo@40 121 Especially, the main concepts are similar in all of them.
meillo@40 122 McIlroy's definition can surely be called the core of the Unix Philosophy,
meillo@40 123 but the fundamental idea behind it all, is ``small is beautiful''.
meillo@40 124
meillo@40 125 .PP
meillo@45 126 The Unix Philosophy explains how to design good software for Unix.
meillo@45 127 Many concepts described here, base on facilities of Unix.
meillo@40 128 Other operating systems may not offer such facilities,
meillo@41 129 hence it may not be possible to design software in the way of the
meillo@41 130 Unix Philosophy for them.
meillo@40 131 .PP
meillo@41 132 The Unix Philosophy has an idea of how the process of software development
meillo@41 133 should look like, but large parts of the philosophy are quite independent
meillo@45 134 from a concrete development process.
meillo@41 135 However, one will soon recognize that some development processes work well
meillo@41 136 with the ideas of the Unix Philosophy and support them, while others are
meillo@41 137 at cross-purposes.
meillo@45 138 Kent Beck's books about Extreme Programming are valuable supplemental
meillo@45 139 resources on this topic.
meillo@1 140 .PP
meillo@41 141 The question of how to actually write code and how the code should looks
meillo@45 142 like in detail, are out of focus here.
meillo@41 143 ``The Practice of Programming'' by Kernighan and Pike,
meillo@41 144 .[
meillo@44 145 kernighan pike
meillo@44 146 practice of programming
meillo@41 147 .]
meillo@41 148 is a good book that covers this topic.
meillo@41 149 Its point of view matches to the one of this paper.
meillo@0 150
meillo@48 151 .H 1 "Importance of software design in general
meillo@0 152 .LP
meillo@40 153 Software design is the planning of how the internal structure
meillo@40 154 and external interfaces of a software should look like.
meillo@39 155 It has nothing to do with visual appearance.
meillo@39 156 If we take a program as a car, then its color is of no matter.
meillo@39 157 Its design would be the car's size, its shape, the locations of doors,
meillo@45 158 the passenger/space ratio, the available controls and instruments,
meillo@45 159 and so forth.
meillo@39 160 .PP
meillo@39 161 Why should software get designed at all?
meillo@6 162 It is general knowledge, that even a bad plan is better than no plan.
meillo@39 163 Not designing software means programming without plan.
meillo@39 164 This will pretty sure lead to horrible results.
meillo@45 165 Software that is horrible to use and horrible to maintain.
meillo@39 166 These two aspects are the visible ones.
meillo@45 167 Often invisible though, are the wasted possible gains.
meillo@39 168 Good software design can make these gains available.
meillo@2 169 .PP
meillo@39 170 A software's design deals with quality properties.
meillo@39 171 Good design leads to good quality, and quality is important.
meillo@39 172 Any car may be able to drive from A to B,
meillo@39 173 but it depends on the car's properties whether it is a good choice
meillo@39 174 for passenger transport or not.
meillo@39 175 It depends on its properties if it is a good choice
meillo@39 176 for a rough mountain area.
meillo@39 177 And it depends on its properties if the ride will be fun.
meillo@39 178
meillo@2 179 .PP
meillo@39 180 Requirements for a software are twofold:
meillo@39 181 functional and non-functional.
meillo@39 182 .IP \(bu
meillo@39 183 Functional requirements define directly the software's functions.
meillo@39 184 They are the reason why software gets written.
meillo@39 185 Someone has a problem and needs a tool to solve it.
meillo@39 186 Being able to solve the problem is the main functional goal.
meillo@39 187 It is the driving force behind all programming effort.
meillo@39 188 Functional requirements are easier to define and to verify.
meillo@39 189 .IP \(bu
meillo@45 190 Non-functional requirements are called \fIquality\fP requirements, too.
meillo@39 191 The quality of a software are the properties that are not directly related to
meillo@39 192 the software's basic functions.
meillo@45 193 Tools of bad quality often do solve the problems they were written for,
meillo@39 194 but introduce problems and difficulties for usage and development, later on.
meillo@39 195 Quality aspects are often overlooked at first sight,
meillo@45 196 and are often difficult to define clearly and to verify.
meillo@2 197 .PP
meillo@45 198 Quality is hardly interesting when the software gets built initially,
meillo@45 199 but it has a high impact on usability and maintenance of the software, later.
meillo@45 200 A short-sighted might see in developing a software, mainly building something up.
meillo@39 201 But experience shows, that building the software the first time is
meillo@39 202 only a small amount of the overall work.
meillo@45 203 Bug fixing, extending, rebuilding of parts \(en maintenance work \(en
meillo@6 204 does soon take over the major part of the time spent on a software.
meillo@45 205 And of course, the time spent actually using the software.
meillo@6 206 These processes are highly influenced by the software's quality.
meillo@39 207 Thus, quality must not be neglected.
meillo@45 208 However, the problem with quality is that you hardly ``stumble over''
meillo@39 209 bad quality during the first build,
meillo@45 210 although this is the time when you should care about good quality most.
meillo@6 211 .PP
meillo@45 212 Software design has little to do with the basic function of a software \(en
meillo@39 213 this requirement will get satisfied anyway.
meillo@39 214 Software design is more about quality aspects of the software.
meillo@39 215 Good design leads to good quality, bad design to bad quality.
meillo@6 216 The primary functions of the software will be affected modestly by bad quality,
meillo@39 217 but good quality can provide a lot of additional gain,
meillo@6 218 even at places where one never expected it.
meillo@6 219 .PP
meillo@45 220 The ISO/IEC\|9126-1 standard, part\|1,
meillo@6 221 .[
meillo@44 222 iso product quality
meillo@6 223 .]
meillo@6 224 defines the quality model as consisting out of:
meillo@6 225 .IP \(bu
meillo@6 226 .I Functionality
meillo@6 227 (suitability, accuracy, inter\%operability, security)
meillo@6 228 .IP \(bu
meillo@6 229 .I Reliability
meillo@6 230 (maturity, fault tolerance, recoverability)
meillo@6 231 .IP \(bu
meillo@6 232 .I Usability
meillo@6 233 (understandability, learnability, operability, attractiveness)
meillo@6 234 .IP \(bu
meillo@6 235 .I Efficiency
meillo@9 236 (time behavior, resource utilization)
meillo@6 237 .IP \(bu
meillo@6 238 .I Maintainability
meillo@23 239 (analyzability, changeability, stability, testability)
meillo@6 240 .IP \(bu
meillo@6 241 .I Portability
meillo@6 242 (adaptability, installability, co-existence, replaceability)
meillo@6 243 .LP
meillo@39 244 Good design can improve these properties of a software,
meillo@45 245 bad designed software likely suffers in these points.
meillo@7 246 .PP
meillo@7 247 One further goal of software design is consistency.
meillo@7 248 Consistency eases understanding, working on, and using things.
meillo@39 249 Consistent internal structure and consistent interfaces to the outside
meillo@39 250 can be provided by good design.
meillo@7 251 .PP
meillo@39 252 Software should be well designed because good design avoids many
meillo@45 253 problems during a software's lifetime.
meillo@39 254 And software should be well designed because good design can offer
meillo@39 255 much additional gain.
meillo@39 256 Indeed, much effort should be spent into good design to make software more valuable.
meillo@39 257 The Unix Philosophy shows a way of how to design software well.
meillo@7 258 It offers guidelines to achieve good quality and high gain for the effort spent.
meillo@0 259
meillo@0 260
meillo@48 261 .H 1 "The Unix Philosophy
meillo@4 262 .LP
meillo@4 263 The origins of the Unix Philosophy were already introduced.
meillo@8 264 This chapter explains the philosophy, oriented on Gancarz,
meillo@8 265 and shows concrete examples of its application.
meillo@5 266
meillo@48 267 .H 2 Pipes
meillo@4 268 .LP
meillo@4 269 Following are some examples to demonstrate how applied Unix Philosophy feels like.
meillo@4 270 Knowledge of using the Unix shell is assumed.
meillo@4 271 .PP
meillo@4 272 Counting the number of files in the current directory:
meillo@41 273 .DS
meillo@4 274 ls | wc -l
meillo@4 275 .DE
meillo@4 276 The
meillo@4 277 .CW ls
meillo@4 278 command lists all files in the current directory, one per line,
meillo@4 279 and
meillo@4 280 .CW "wc -l
meillo@8 281 counts the number of lines.
meillo@4 282 .PP
meillo@8 283 Counting the number of files that do not contain ``foo'' in their name:
meillo@41 284 .DS
meillo@4 285 ls | grep -v foo | wc -l
meillo@4 286 .DE
meillo@4 287 Here, the list of files is filtered by
meillo@4 288 .CW grep
meillo@45 289 to remove all lines that contain ``foo''.
meillo@45 290 The rest equals the previous example.
meillo@4 291 .PP
meillo@4 292 Finding the five largest entries in the current directory.
meillo@41 293 .DS
meillo@4 294 du -s * | sort -nr | sed 5q
meillo@4 295 .DE
meillo@4 296 .CW "du -s *
meillo@45 297 returns the recursively summed sizes of all files in the current directory
meillo@8 298 \(en no matter if they are regular files or directories.
meillo@4 299 .CW "sort -nr
meillo@45 300 sorts the list numerically in reverse order (descending).
meillo@4 301 Finally,
meillo@4 302 .CW "sed 5q
meillo@4 303 quits after it has printed the fifth line.
meillo@4 304 .PP
meillo@4 305 The presented command lines are examples of what Unix people would use
meillo@4 306 to get the desired output.
meillo@4 307 There are also other ways to get the same output.
meillo@4 308 It's a user's decision which way to go.
meillo@14 309 .PP
meillo@8 310 The examples show that many tasks on a Unix system
meillo@4 311 are accomplished by combining several small programs.
meillo@4 312 The connection between the single programs is denoted by the pipe operator `|'.
meillo@4 313 .PP
meillo@4 314 Pipes, and their extensive and easy use, are one of the great
meillo@4 315 achievements of the Unix system.
meillo@4 316 Pipes between programs have been possible in earlier operating systems,
meillo@4 317 but it has never been a so central part of the concept.
meillo@45 318 When, in the early seventies, Doug McIlroy introduced pipes into the
meillo@4 319 Unix system,
meillo@4 320 ``it was this concept and notation for linking several programs together
meillo@4 321 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
meillo@4 322 .[
meillo@44 323 aughenbaugh
meillo@44 324 unix oral history
meillo@45 325 .]
meillo@4 326 .PP
meillo@4 327 Being able to specify pipelines in an easy way is,
meillo@4 328 however, not enough by itself.
meillo@5 329 It is only one half.
meillo@4 330 The other is the design of the programs that are used in the pipeline.
meillo@45 331 They need interfaces that allow them to be used in such a way.
meillo@5 332
meillo@48 333 .H 2 "Interface design
meillo@5 334 .LP
meillo@11 335 Unix is, first of all, simple \(en Everything is a file.
meillo@5 336 Files are sequences of bytes, without any special structure.
meillo@45 337 Programs should be filters, which read a stream of bytes from standard input (stdin)
meillo@45 338 and write a stream of bytes to standard output (stdout).
meillo@8 339 If the files \fIare\fP sequences of bytes,
meillo@8 340 and the programs \fIare\fP filters on byte streams,
meillo@45 341 then there is exactly one data interface.
meillo@45 342 Hence it is possible to combine programs in any desired way.
meillo@5 343 .PP
meillo@45 344 Even a handful of small programs yields a large set of combinations,
meillo@5 345 and thus a large set of different functions.
meillo@5 346 This is leverage!
meillo@5 347 If the programs are orthogonal to each other \(en the best case \(en
meillo@5 348 then the set of different functions is greatest.
meillo@5 349 .PP
meillo@45 350 Programs can also have a separate control interface,
meillo@11 351 besides their data interface.
meillo@11 352 The control interface is often called ``user interface'',
meillo@11 353 because it is usually designed to be used by humans.
meillo@11 354 The Unix Philosophy discourages to assume the user to be human.
meillo@11 355 Interactive use of software is slow use of software,
meillo@11 356 because the program waits for user input most of the time.
meillo@45 357 Interactive software requires the user to be in front of the computer.
meillo@11 358 Interactive software occupy the user's attention while they are running.
meillo@11 359 .PP
meillo@45 360 Now to come back to the idea of combining several small programs,
meillo@11 361 to have a more specific function.
meillo@11 362 If these single tools would all be interactive,
meillo@11 363 how would the user control them?
meillo@45 364 It is not only a problem to control several programs at once,
meillo@45 365 if they run at the same time,
meillo@11 366 it also very inefficient to have to control each of the single programs
meillo@45 367 that are intended to act as one large program.
meillo@11 368 Hence, the Unix Philosophy discourages programs to demand interactive use.
meillo@11 369 The behavior of programs should be defined at invocation.
meillo@45 370 This is done by specifying arguments to the program call
meillo@45 371 (command line switches).
meillo@11 372 Gancarz discusses this topic as ``avoid captive user interfaces''.
meillo@46 373 .[ [
meillo@44 374 gancarz unix philosophy
meillo@46 375 .], page 88 ff.]
meillo@11 376 .PP
meillo@11 377 Non-interactive use is, during development, also an advantage for testing.
meillo@11 378 Testing of interactive programs is much more complicated,
meillo@11 379 than testing of non-interactive programs.
meillo@5 380
meillo@48 381 .H 2 "The toolchest approach
meillo@5 382 .LP
meillo@5 383 A toolchest is a set of tools.
meillo@5 384 Instead of having one big tool for all tasks, one has many small tools,
meillo@5 385 each for one task.
meillo@5 386 Difficult tasks are solved by combining several of the small, simple tools.
meillo@5 387 .PP
meillo@11 388 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs
meillo@11 389 that are filters on byte streams.
meillo@11 390 They are, to a large extend, unrelated in their function.
meillo@11 391 Hence, the Unix toolchest provides a large set of functions
meillo@11 392 that can be accessed by combining the programs in the desired way.
meillo@11 393 .PP
meillo@11 394 There are also advantages for developing small toolchest programs.
meillo@5 395 It is easier and less error-prone to write small programs.
meillo@5 396 It is also easier and less error-prone to write a large set of small programs,
meillo@5 397 than to write one large program with all the functionality included.
meillo@5 398 If the small programs are combinable, then they offer even a larger set
meillo@5 399 of functions than the single large program.
meillo@45 400 Hence, one gets two advantages out of writing small, combinable programs:
meillo@45 401 They are easier to write and they offer a greater set of functions through
meillo@45 402 combination.
meillo@5 403 .PP
meillo@45 404 But there are also two main drawbacks of the toolchest approach.
meillo@45 405 First, one simple, standardized interface has to be sufficient.
meillo@5 406 If one feels the need for more ``logic'' than a stream of bytes,
meillo@8 407 then a different approach might be of need.
meillo@13 408 But it is also possible, that he just can not imagine a design where
meillo@8 409 a stream of bytes is sufficient.
meillo@8 410 By becoming more familiar with the ``Unix style of thinking'',
meillo@8 411 developers will more often and easier find simple designs where
meillo@8 412 a stream of bytes is a sufficient interface.
meillo@8 413 .PP
meillo@8 414 The second drawback of a toolchest affects the users.
meillo@45 415 A toolchest is often more difficult to use.
meillo@9 416 It is necessary to become familiar with each of the tools,
meillo@5 417 to be able to use the right one in a given situation.
meillo@45 418 Additionally, one needs to combine the tools in a senseful way himself.
meillo@45 419 This is like a sharp knife \(en it is a powerful tool in the hand of a
meillo@45 420 master, but of no good value in the hand of an unskilled.
meillo@45 421 However, learning single, small tools of a toolchest is easier than
meillo@45 422 learning a complex tool.
meillo@45 423 And the user will already have a basic understanding of a yet unknown tool,
meillo@45 424 if the tools of a toolchest have a common, consistent style.
meillo@45 425 He will be able to transfer knowledge over from one tool to another.
meillo@5 426 .PP
meillo@45 427 Moreover, the second drawback can be removed to a large extend
meillo@45 428 by adding wrappers around the basic tools.
meillo@45 429 Novice users do not need to learn several tools, if a professional wraps
meillo@45 430 complete command lines into a higher-level script.
meillo@5 431 Note that the wrapper script still calls the small tools;
meillo@45 432 it is just like a skin around them.
meillo@45 433 No complexity is added this way.
meillo@45 434 But new programs can get created out of existing one with very low effort.
meillo@5 435 .PP
meillo@5 436 A wrapper script for finding the five largest entries in the current directory
meillo@5 437 could look like this:
meillo@41 438 .DS
meillo@5 439 #!/bin/sh
meillo@5 440 du -s * | sort -nr | sed 5q
meillo@5 441 .DE
meillo@45 442 The script itself is just a text file that calls the command line,
meillo@45 443 which a professional user would type in directly.
meillo@45 444 It is probably worth to make the program flexible on the number of
meillo@45 445 entries it prints:
meillo@41 446 .DS
meillo@8 447 #!/bin/sh
meillo@8 448 num=5
meillo@8 449 [ $# -eq 1 ] && num="$1"
meillo@8 450 du -sh * | sort -nr | sed "${num}q"
meillo@8 451 .DE
meillo@8 452 This script acts like the one before, when called without an argument.
meillo@8 453 But one can also specify a numerical argument to define the number of lines to print.
meillo@45 454 One can surely imagine even more flexible versions, however,
meillo@45 455 they will still relay on the external programs,
meillo@45 456 which do the actual work.
meillo@5 457
meillo@48 458 .H 2 "A powerful shell
meillo@8 459 .LP
meillo@45 460 The Unix shell provides the possibility to combine small programs into large ones.
meillo@45 461 But a powerful shell is a great feature in other ways, too.
meillo@45 462 For instance by being scriptable.
meillo@45 463 Control statements are build into the shell.
meillo@45 464 The functions, however, are the normal programs of the system.
meillo@45 465 Thus, as the programs are already known,
meillo@45 466 learning to program in the shell becomes easy.
meillo@8 467 Using normal programs as functions in the shell programming language
meillo@10 468 is only possible because they are small and combinable tools in a toolchest style.
meillo@8 469 .PP
meillo@45 470 The Unix shell encourages to write small scripts,
meillo@45 471 by combining existing programs, because it is so easy to do.
meillo@8 472 This is a great step towards automation.
meillo@8 473 It is wonderful if the effort to automate a task equals the effort
meillo@45 474 to do the task a second time by hand.
meillo@45 475 If this holds,
meillo@45 476 then the user will be happy to automate everything he does more than once.
meillo@8 477 .PP
meillo@8 478 Small programs that do one job well, standardized interfaces between them,
meillo@8 479 a mechanism to combine parts to larger parts, and an easy way to automate tasks,
meillo@8 480 this will inevitably produce software leverage.
meillo@8 481 Getting multiple times the benefit of an investment is a great offer.
meillo@10 482 .PP
meillo@10 483 The shell also encourages rapid prototyping.
meillo@10 484 Many well known programs started as quickly hacked shell scripts,
meillo@10 485 and turned into ``real'' programs, written in C, later.
meillo@45 486 Building a prototype first, is a way to avoid the biggest problems
meillo@10 487 in application development.
meillo@45 488 Fred Brooks explains in ``No Silver Bullet'':
meillo@10 489 .[
meillo@44 490 brooks
meillo@44 491 no silver bullet
meillo@10 492 .]
meillo@10 493 .QP
meillo@10 494 The hardest single part of building a software system is deciding precisely what to build.
meillo@10 495 No other part of the conceptual work is so difficult as establishing the detailed
meillo@10 496 technical requirements, [...].
meillo@10 497 No other part of the work so cripples the resulting system if done wrong.
meillo@10 498 No other part is more difficult to rectify later.
meillo@10 499 .PP
meillo@45 500 Writing a prototype is a great method for becoming familiar with the requirements
meillo@45 501 and to run into real problems early.
meillo@47 502 .[ [
meillo@47 503 gancarz
meillo@47 504 unix philosophy
meillo@47 505 .], page 28 f.]
meillo@45 506 .PP
meillo@45 507 Prototyping is often seen as a first step in building a software.
meillo@10 508 This is, of course, good.
meillo@10 509 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping:
meillo@10 510 After having built the prototype, one might notice, that the prototype is already
meillo@10 511 \fIgood enough\fP.
meillo@45 512 Hence, no reimplementation, in a more sophisticated programming language,
meillo@45 513 might be of need, at least for the moment.
meillo@23 514 Maybe later, it might be necessary to rewrite the software, but not now.
meillo@45 515 By delaying further work, one keeps the flexibility to react on
meillo@10 516 changing requirements.
meillo@10 517 Software parts that are not written will not miss the requirements.
meillo@10 518
meillo@48 519 .H 2 "Worse is better
meillo@10 520 .LP
meillo@45 521 The Unix Philosophy aims for the 90% solution;
meillo@10 522 others call it the ``Worse is better'' approach.
meillo@47 523 Experience from real life projects shows:
meillo@10 524 .PP
meillo@45 525 (1) It is almost never possible to define the
meillo@10 526 requirements completely and correctly the first time.
meillo@45 527 Hence one should not try to; one will fail anyway.
meillo@45 528 .PP
meillo@45 529 (2) Requirements change during time.
meillo@10 530 Hence it is best to delay requirement-based design decisions as long as possible.
meillo@45 531 The software should be small and flexible as long as possible
meillo@10 532 to react on changing requirements.
meillo@10 533 Shell scripts, for example, are more easily adjusted as C programs.
meillo@45 534 .PP
meillo@45 535 (3) Maintenance work is hard work.
meillo@45 536 Hence, one should keep the amount of code as small as possible;
meillo@10 537 it should just fulfill the \fIcurrent\fP requirements.
meillo@45 538 Software parts that will be written in future,
meillo@45 539 do not need maintenance till then.
meillo@10 540 .PP
meillo@47 541 See Brooks' ``The Mythical Man-Month'' for reference.
meillo@47 542 .[ [
meillo@47 543 brooks
meillo@47 544 mythical man-month
meillo@47 545 .], page 115 ff.]
meillo@47 546 .PP
meillo@10 547 Starting with a prototype in a scripting language has several advantages:
meillo@10 548 .IP \(bu
meillo@10 549 As the initial effort is low, one will likely start right away.
meillo@10 550 .IP \(bu
meillo@10 551 As working parts are available soon, the real requirements can get identified soon.
meillo@10 552 .IP \(bu
meillo@45 553 When a software is usable and valuable, it gets used, and thus tested.
meillo@10 554 Hence problems will be found at early stages of the development.
meillo@10 555 .IP \(bu
meillo@10 556 The prototype might be enough for the moment,
meillo@45 557 thus further work on the software can get delayed to a time
meillo@10 558 when one knows better about the requirements and problems,
meillo@10 559 than now.
meillo@10 560 .IP \(bu
meillo@45 561 Implementing now only the parts that are actually needed at the moment,
meillo@45 562 introduces fewer programming and maintenance work.
meillo@10 563 .IP \(bu
meillo@10 564 If the global situation changes so that the software is not needed anymore,
meillo@10 565 then less effort was spent into the project, than it would have be
meillo@10 566 when a different approach had been used.
meillo@10 567
meillo@48 568 .H 2 "Upgrowth and survival of software
meillo@11 569 .LP
meillo@12 570 So far it was talked about \fIwriting\fP or \fIbuilding\fP software.
meillo@13 571 Although these are just verbs, they do imply a specific view on the work process
meillo@13 572 they describe.
meillo@12 573 The better verb, however, is to \fIgrow\fP.
meillo@12 574 Creating software in the sense of the Unix Philosophy is an incremental process.
meillo@12 575 It starts with a first prototype, which evolves as requirements change.
meillo@12 576 A quickly hacked shell script might become a large, sophisticated,
meillo@13 577 compiled program this way.
meillo@13 578 Its lifetime begins with the initial prototype and ends when the software is not used anymore.
meillo@45 579 While being alive it will get extended, rearranged, rebuilt.
meillo@12 580 Growing software matches the view that ``software is never finished. It is only released.''
meillo@46 581 .[ [
meillo@44 582 gancarz
meillo@44 583 unix philosophy
meillo@46 584 .], page 26]
meillo@12 585 .PP
meillo@13 586 Software can be seen as being controlled by evolutionary processes.
meillo@13 587 Successful software is software that is used by many for a long time.
meillo@12 588 This implies that the software is needed, useful, and better than alternatives.
meillo@12 589 Darwin talks about: ``The survival of the fittest.''
meillo@12 590 .[
meillo@44 591 darwin
meillo@44 592 origin of species
meillo@12 593 .]
meillo@12 594 Transferred to software: The most successful software, is the fittest,
meillo@12 595 is the one that survives.
meillo@13 596 (This may be at the level of one creature, or at the level of one species.)
meillo@13 597 The fitness of software is affected mainly by four properties:
meillo@15 598 portability of code, portability of data, range of usability, and reusability of parts.
meillo@13 599 .PP
meillo@15 600 (1)
meillo@15 601 .I "Portability of code
meillo@15 602 means, using high-level programming languages,
meillo@13 603 sticking to the standard,
meillo@47 604 .[ [
meillo@47 605 kernighan pike
meillo@47 606 practice of programming
meillo@47 607 .], chapter\|8]
meillo@13 608 and avoiding optimizations that introduce dependencies on specific hardware.
meillo@13 609 Hardware has a much lower lifetime than software.
meillo@13 610 By chaining software to a specific hardware,
meillo@13 611 the software's lifetime gets shortened to that of this hardware.
meillo@13 612 In contrast, software should be easy to port \(en
meillo@23 613 adaptation is the key to success.
meillo@13 614 .PP
meillo@15 615 (2)
meillo@15 616 .I "Portability of data
meillo@15 617 is best achieved by avoiding binary representations
meillo@13 618 to store data, because binary representations differ from machine to machine.
meillo@23 619 Textual representation is favored.
meillo@45 620 Historically, \s-1ASCII\s0 was the charset of choice.
meillo@45 621 For the future, \s-1UTF\s0-8 might be the better choice.
meillo@13 622 Important is that it is a plain text representation in a
meillo@13 623 very common charset encoding.
meillo@13 624 Apart from being able to transfer data between machines,
meillo@45 625 readable data has the great advantage, that humans are able to directly
meillo@45 626 read and edit it with text editors and other tools from the Unix toolchest.
meillo@47 627 .[ [
meillo@47 628 gancarz
meillo@47 629 unix philosophy
meillo@47 630 .], page 56 ff.]
meillo@13 631 .PP
meillo@15 632 (3)
meillo@15 633 A large
meillo@15 634 .I "range of usability
meillo@23 635 ensures good adaptation, and thus good survival.
meillo@13 636 It is a special distinction if a software becomes used in fields of action,
meillo@13 637 the original authors did never imagine.
meillo@13 638 Software that solves problems in a general way will likely be used
meillo@45 639 for many kinds of similar problems.
meillo@45 640 Being too specific limits the range of usability.
meillo@13 641 Requirements change through time, thus use cases change or even vanish.
meillo@45 642 As a good example in this point,
meillo@13 643 Allman identifies flexibility to be one major reason for sendmail's success:
meillo@13 644 .[
meillo@44 645 allman
meillo@44 646 sendmail
meillo@13 647 .]
meillo@13 648 .QP
meillo@13 649 Second, I limited myself to the routing function [...].
meillo@13 650 This was a departure from the dominant thought of the time, [...].
meillo@13 651 .QP
meillo@45 652 Third, the sendmail configuration file was flexible enough to adapt
meillo@13 653 to a rapidly changing world [...].
meillo@12 654 .LP
meillo@45 655 Successful software adapts itself to the changing world.
meillo@13 656 .PP
meillo@15 657 (4)
meillo@15 658 .I "Reuse of parts
meillo@15 659 is even one step further.
meillo@13 660 A software may completely lose its field of action,
meillo@13 661 but parts of which the software is build may be general and independent enough
meillo@13 662 to survive this death.
meillo@13 663 If software is build by combining small independent programs,
meillo@45 664 then these parts are readily available for reuse.
meillo@13 665 Who cares if the large program is a failure,
meillo@13 666 but parts of it become successful instead?
meillo@10 667
meillo@48 668 .H 2 "Summary
meillo@0 669 .LP
meillo@45 670 This chapter explained central ideas of the Unix Philosophy.
meillo@45 671 For each of the ideas, the advantages they introduce were explained.
meillo@45 672 The Unix Philosophy are guidelines that help to write more valuable software.
meillo@14 673 From the view point of a software developer or software designer,
meillo@14 674 the Unix Philosophy provides answers to many software design problem.
meillo@14 675 .PP
meillo@14 676 The various ideas of the Unix Philosophy are very interweaved
meillo@14 677 and can hardly be applied independently.
meillo@14 678 However, the probably most important messages are:
meillo@45 679 .I "``Keep it simple!''" ,
meillo@14 680 .I "``Do one thing well!''" ,
meillo@14 681 and
meillo@14 682 .I "``Use software leverage!''
meillo@0 683
meillo@8 684
meillo@8 685
meillo@48 686 .H 1 "Case study: \s-1MH\s0
meillo@18 687 .LP
meillo@30 688 The previous chapter introduced and explained the Unix Philosophy
meillo@18 689 from a general point of view.
meillo@30 690 The driving force were the guidelines; references to
meillo@18 691 existing software were given only sparsely.
meillo@18 692 In this and the next chapter, concrete software will be
meillo@18 693 the driving force in the discussion.
meillo@18 694 .PP
meillo@23 695 This first case study is about the mail user agents (\s-1MUA\s0)
meillo@23 696 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP
meillo@23 697 (``new mail handler'').
meillo@47 698 .[
meillo@47 699 nmh website
meillo@47 700 .]
meillo@23 701 \s-1MUA\s0s provide functions to read, compose, and organize mail,
meillo@45 702 but (ideally) not to transfer it.
meillo@45 703 In this document, the name \s-1MH\s0 will be used to include nmh.
meillo@19 704 A distinction will only be made if differences between
meillo@45 705 \s-1MH\s0 and nmh are described.
meillo@18 706
meillo@0 707
meillo@48 708 .H 2 "Historical background
meillo@0 709 .LP
meillo@19 710 Electronic mail was available in Unix very early.
meillo@30 711 The first \s-1MUA\s0 on Unix was \f(CWmail\fP,
meillo@30 712 which was already present in the First Edition.
meillo@46 713 .[ [
meillo@44 714 salus
meillo@44 715 quarter century of unix
meillo@46 716 .], page 41 f.]
meillo@45 717 It was a small program that either printed the user's mailbox file
meillo@45 718 or appended text to someone elses mailbox file,
meillo@19 719 depending on the command line arguments.
meillo@19 720 .[
meillo@44 721 manual mail(1)
meillo@19 722 .]
meillo@19 723 It was a program that did one job well.
meillo@23 724 This job was emailing, which was very simple then.
meillo@19 725 .PP
meillo@23 726 Later, emailing became more powerful, and thus more complex.
meillo@19 727 The simple \f(CWmail\fP, which knew nothing of subjects,
meillo@19 728 independent handling of single messages,
meillo@45 729 and long-time email storage, was not powerful enough anymore.
meillo@45 730 In 1978 at Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M')
meillo@45 731 to provide additional functions for emailing.
meillo@19 732 Mail was still one program, but now it was large and did
meillo@19 733 several jobs.
meillo@23 734 Its user interface is modeled after the one of \fIed\fP.
meillo@19 735 It is designed for humans, but is still scriptable.
meillo@23 736 \fImailx\fP is the adaptation of Berkeley Mail into System V.
meillo@19 737 .[
meillo@44 738 ritter
meillo@44 739 mailx history
meillo@19 740 .]
meillo@30 741 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s
meillo@19 742 followed Mail's direction.
meillo@19 743 They are large, monolithic programs which include all emailing functions.
meillo@19 744 .PP
meillo@23 745 A different way was taken by the people of \s-1RAND\s0 Corporation.
meillo@38 746 In the beginning, they also had used a monolithic mail system,
meillo@30 747 called \s-1MS\s0 (for ``mail system'').
meillo@19 748 But in 1977, Stockton Gaines and Norman Shapiro
meillo@19 749 came up with a proposal of a new email system concept \(en
meillo@45 750 one that honored the Unix Philosophy.
meillo@19 751 The concept was implemented by Bruce Borden in 1978 and 1979.
meillo@19 752 This was the birth of \s-1MH\s0 \(en the ``mail handler''.
meillo@18 753 .PP
meillo@18 754 Since then, \s-1RAND\s0, the University of California at Irvine and
meillo@19 755 at Berkeley, and several others have contributed to the software.
meillo@18 756 However, it's core concepts remained the same.
meillo@23 757 In the late 90s, when development of \s-1MH\s0 slowed down,
meillo@19 758 Richard Coleman started with \fInmh\fP, the new mail handler.
meillo@45 759 His goal was to improve \s-1MH\s0 especially in regard of
meillo@23 760 the requirements of modern emailing.
meillo@19 761 Today, nmh is developed by various people on the Internet.
meillo@18 762 .[
meillo@44 763 ware
meillo@44 764 rand history
meillo@18 765 .]
meillo@18 766 .[
meillo@44 767 peek
meillo@44 768 mh
meillo@18 769 .]
meillo@0 770
meillo@48 771 .H 2 "Contrasts to monolithic mail systems
meillo@0 772 .LP
meillo@19 773 All \s-1MUA\s0s are monolithic, except \s-1MH\s0.
meillo@38 774 Although there might actually exist further, very little known,
meillo@30 775 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well.
meillo@19 776 .PP
meillo@30 777 Monolithic \s-1MUA\s0s gather all their functions in one program.
meillo@30 778 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job.
meillo@23 779 Following is a list of important programs of \s-1MH\s0's toolchest
meillo@30 780 and their function.
meillo@30 781 It gives a feeling of how the toolchest looks like.
meillo@19 782 .IP \(bu
meillo@19 783 .CW inc :
meillo@30 784 incorporate new mail (this is how mail enters the system)
meillo@19 785 .IP \(bu
meillo@19 786 .CW scan :
meillo@19 787 list messages in folder
meillo@19 788 .IP \(bu
meillo@19 789 .CW show :
meillo@19 790 show message
meillo@19 791 .IP \(bu
meillo@19 792 .CW next\fR/\fPprev :
meillo@19 793 show next/previous message
meillo@19 794 .IP \(bu
meillo@19 795 .CW folder :
meillo@19 796 change current folder
meillo@19 797 .IP \(bu
meillo@19 798 .CW refile :
meillo@45 799 refile message into different folder
meillo@19 800 .IP \(bu
meillo@19 801 .CW rmm :
meillo@19 802 remove message
meillo@19 803 .IP \(bu
meillo@19 804 .CW comp :
meillo@45 805 compose new message
meillo@19 806 .IP \(bu
meillo@19 807 .CW repl :
meillo@45 808 reply to message
meillo@19 809 .IP \(bu
meillo@19 810 .CW forw :
meillo@45 811 forward message
meillo@19 812 .IP \(bu
meillo@19 813 .CW send :
meillo@45 814 send prepared message (this is how mail leaves the system)
meillo@0 815 .LP
meillo@19 816 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have.
meillo@19 817 The user does not leave the shell to run \s-1MH\s0,
meillo@45 818 instead he uses the various \s-1MH\s0 programs within the shell.
meillo@23 819 Using a monolithic program with a captive user interface
meillo@23 820 means ``entering'' the program, using it, and ``exiting'' the program.
meillo@23 821 Using toolchests like \s-1MH\s0 means running programs,
meillo@45 822 alone or in combination with others, also from other toolchests,
meillo@23 823 without leaving the shell.
meillo@30 824
meillo@48 825 .H 2 "Data storage
meillo@30 826 .LP
meillo@34 827 \s-1MH\s0's mail storage is a directory tree under the user's
meillo@34 828 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP),
meillo@34 829 where mail folders are directories and mail messages are text files
meillo@34 830 within them.
meillo@34 831 Each mail folder contains a file \f(CW.mh_sequences\fP which lists
meillo@45 832 the public message sequences of that folder,
meillo@45 833 for instance the \fIunseen\fP sequence for new messages.
meillo@34 834 Mail messages are text files located in a mail folder.
meillo@34 835 The files contain the messages as they were received.
meillo@45 836 They are named by ascending numbers in each folder.
meillo@19 837 .PP
meillo@30 838 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0.
meillo@30 839 Alternatives are \fImbox\fP and \fImaildir\fP.
meillo@30 840 In the mbox format all messages are stored within one file.
meillo@30 841 This was a good solution in the early days, when messages
meillo@30 842 were only a few lines of text and were deleted soon.
meillo@30 843 Today, when single messages often include several megabytes
meillo@30 844 of attachments, it is a bad solution.
meillo@30 845 Another disadvantage of the mbox format is that it is
meillo@30 846 more difficult to write tools that work on mail messages,
meillo@30 847 because it is always necessary to first find and extract
meillo@30 848 the relevant message in the mbox file.
meillo@45 849 With the \s-1MH\s0 mailbox format, each message is a separate file.
meillo@30 850 Also, the problem of concurrent access to one mailbox is
meillo@30 851 reduced to the problem of concurrent access to one message.
meillo@45 852 The maildir format is generally similar to the \s-1MH\s0 format,
meillo@30 853 but modified towards guaranteed reliability.
meillo@30 854 This involves some complexity, unfortunately.
meillo@34 855 .PP
meillo@34 856 Working with \s-1MH\s0's toolchest on mailboxes is much like
meillo@34 857 working with Unix' toolchest on directory trees:
meillo@34 858 \f(CWscan\fP is like \f(CWls\fP,
meillo@34 859 \f(CWshow\fP is like \f(CWcat\fP,
meillo@34 860 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP,
meillo@34 861 \f(CWrefile\fP is like \f(CWmv\fP,
meillo@34 862 and \f(CWrmm\fP is like \f(CWrm\fP.
meillo@34 863 .PP
meillo@45 864 \s-1MH\s0 extends the context of processes in Unix by two more items,
meillo@45 865 for its tools:
meillo@34 866 .IP \(bu
meillo@34 867 The current mail folder, which is similar to the current working directory.
meillo@34 868 For mail folders, \f(CWfolder\fP provides the corresponding functionality
meillo@34 869 of \f(CWcd\fP and \f(CWpwd\fP for directories.
meillo@34 870 .IP \(bu
meillo@34 871 Sequences, which are named sets of messages in a mail folder.
meillo@34 872 The current message, relative to a mail folder, is a special sequence.
meillo@34 873 It enables commands like \f(CWnext\fP and \f(CWprev\fP.
meillo@34 874 .LP
meillo@45 875 In contrast to Unix' context, which is maintained by the kernel,
meillo@45 876 \s-1MH\s0's context must be maintained by the tools themselves.
meillo@45 877 Usually there is one context per user, which resides in his
meillo@45 878 \f(CWcontext\fP file in the \s-1MH\s0 directory,
meillo@45 879 but a user can have several contexts, too.
meillo@45 880 Public sequences are an exception, as they belong to a mail folder,
meillo@45 881 and reside in the \f(CW.mh_sequences\fP file there.
meillo@34 882 .[
meillo@44 883 man page mh-profile mh-sequence
meillo@34 884 .]
meillo@20 885
meillo@48 886 .H 2 "Discussion of the design
meillo@0 887 .LP
meillo@45 888 This section discusses \s-1MH\s0 in regard to the tenets
meillo@45 889 of the Unix Philosophy that Gancarz identified.
meillo@20 890
meillo@20 891 .PP
meillo@33 892 .B "Small is beautiful
meillo@20 893 and
meillo@33 894 .B "do one thing well
meillo@20 895 are two design goals that are directly visible in \s-1MH\s0.
meillo@45 896 Gancarz actually presents \s-1MH\s0 in his book as example under the
meillo@45 897 headline ``Making \s-1UNIX\s0 Do One Thing Well'':
meillo@46 898 .[ [
meillo@44 899 gancarz
meillo@44 900 unix philosophy
meillo@46 901 .], page 125 ff.]
meillo@20 902 .QP
meillo@20 903 [\s-1MH\s0] consists of a series of programs which
meillo@20 904 when combined give the user an enormous ability
meillo@20 905 to manipulate electronic mail messages.
meillo@20 906 A complex application, it shows that not only is it
meillo@20 907 possible to build large applications from smaller
meillo@20 908 components, but also that such designs are actually preferable.
meillo@20 909 .LP
meillo@45 910 The various programs of \s-1MH\s0 were relatively easy to write,
meillo@45 911 because each of them is small, limited to one function,
meillo@23 912 and has clear boundaries.
meillo@20 913 For the same reasons, they are also good to maintain.
meillo@20 914 Further more, the system can easily get extended.
meillo@20 915 One only needs to put a new program into the toolchest.
meillo@23 916 This was done, for instance, when \s-1MIME\s0 support was added
meillo@20 917 (e.g. \f(CWmhbuild\fP).
meillo@20 918 Also, different programs can exist to do the basically same job
meillo@20 919 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP).
meillo@45 920 .PP
meillo@20 921 If someone needs a mail system with some additionally
meillo@45 922 functions that are not available anywhere yet, he best expands a
meillo@45 923 toolchest system like \s-1MH\s0.
meillo@45 924 There he can add new functionality by simply adding additional
meillo@45 925 programs to the toolchest.
meillo@45 926 There he does not risk to break existing functionality by doing so.
meillo@20 927
meillo@20 928 .PP
meillo@34 929 .B "Store data in flat text files
meillo@34 930 is followed by \s-1MH\s0.
meillo@34 931 This is not surprising, because email messages are already plain text.
meillo@34 932 \s-1MH\s0 stores the messages as it receives them,
meillo@45 933 thus any other tool that works on \s-1RFC\s0\|2822 mail messages can operate
meillo@34 934 on the messages in an \s-1MH\s0 mailbox.
meillo@45 935 All other files \s-1MH\s0 uses are plain text, too.
meillo@34 936 It is therefore possible and encouraged to use the text processing
meillo@34 937 tools of Unix' toolchest to extend \s-1MH\s0's toolchest.
meillo@20 938
meillo@20 939 .PP
meillo@33 940 .B "Avoid captive user interfaces" .
meillo@19 941 \s-1MH\s0 is perfectly suited for non-interactive use.
meillo@19 942 It offers all functions directly and without captive user interfaces.
meillo@30 943 If, nonetheless, users want a graphical user interface,
meillo@45 944 they can have it with \fIxmh\fP or \fIexmh\fP.
meillo@19 945 These are graphical frontends for the \s-1MH\s0 toolchest.
meillo@19 946 This means, all email-related work is still done by \s-1MH\s0 tools,
meillo@45 947 but the frontend calls the appropriate commands when the user
meillo@30 948 clicks on buttons.
meillo@45 949 .PP
meillo@20 950 Providing easy-to-use user interfaces in form of frontends is a good
meillo@19 951 approach, because it does not limit the power of the backend itself.
meillo@20 952 The frontend will anyway only be able to make a subset of the
meillo@23 953 backend's power and flexibility available to the user.
meillo@20 954 But if it is a separate program,
meillo@20 955 then the missing parts can still be accessed at the backend directly.
meillo@19 956 If it is integrated, then this will hardly be possible.
meillo@45 957 An additional advantage is the possibility to have different frontends
meillo@45 958 to the same backend.
meillo@19 959
meillo@19 960 .PP
meillo@33 961 .B "Choose portability over efficiency
meillo@20 962 and
meillo@33 963 .B "use shell scripts to increase leverage and portability" .
meillo@20 964 These two tenets are indirectly, but nicely, demonstrated by
meillo@30 965 Bolsky and Korn in their book about the Korn Shell.
meillo@20 966 .[
meillo@44 967 bolsky korn
meillo@44 968 korn shell
meillo@20 969 .]
meillo@45 970 Chapter\|18 of the book shows a basic implementation
meillo@20 971 of a subset of \s-1MH\s0 in ksh scripts.
meillo@45 972 Of course, this is just a demonstration, but a brilliant one.
meillo@20 973 It shows how quickly one can implement such a prototype with shell scripts,
meillo@20 974 and how readable they are.
meillo@20 975 The implementation in the scripting language may not be very fast,
meillo@20 976 but it can be fast enough though, and this is all that matters.
meillo@20 977 By having the code in an interpreted language, like the shell,
meillo@20 978 portability becomes a minor issue, if we assume the interpreter
meillo@20 979 to be widespread.
meillo@45 980 .PP
meillo@20 981 This demonstration also shows how easy it is to create single programs
meillo@20 982 of a toolchest software.
meillo@45 983 Eight tools (two of them have multiple names) and 16 functions
meillo@45 984 with supporting code are presented to the reader.
meillo@45 985 The tools comprise less than 40 lines of ksh each,
meillo@30 986 in total about 200 lines.
meillo@45 987 The functions comprise less than 80 lines of ksh each,
meillo@30 988 in total about 450 lines.
meillo@20 989 Such small software is easy to write, easy to understand,
meillo@20 990 and thus easy to maintain.
meillo@23 991 A toolchest improves the possibility to only write some parts
meillo@20 992 and though create a working result.
meillo@45 993 Expanding the toolchest, even without global changes,
meillo@45 994 will likely be possible.
meillo@20 995
meillo@20 996 .PP
meillo@33 997 .B "Use software leverage to your advantage
meillo@20 998 and the lesser tenet
meillo@33 999 .B "allow the user to tailor the environment
meillo@20 1000 are ideally followed in the design of \s-1MH\s0.
meillo@21 1001 Tailoring the environment is heavily encouraged by the ability to
meillo@30 1002 directly define default options to programs.
meillo@30 1003 It is even possible to define different default options
meillo@45 1004 depending on the name under which a program is called.
meillo@45 1005 Software leverage is heavily encouraged by the ease of
meillo@45 1006 creating shell scripts that run a specific command line,
meillo@30 1007 built of several \s-1MH\s0 programs.
meillo@21 1008 There is few software that so much wants users to tailor their
meillo@21 1009 environment and to leverage the use of the software, like \s-1MH\s0.
meillo@45 1010 .PP
meillo@21 1011 Just to make one example:
meillo@23 1012 One might prefer a different listing format for the \f(CWscan\fP
meillo@21 1013 program.
meillo@30 1014 It is possible to take one of the distributed format files
meillo@21 1015 or to write one yourself.
meillo@21 1016 To use the format as default for \f(CWscan\fP, a single line,
meillo@21 1017 reading
meillo@21 1018 .DS
meillo@21 1019 scan: -form FORMATFILE
meillo@21 1020 .DE
meillo@21 1021 must be added to \f(CW.mh_profile\fP.
meillo@21 1022 If one wants this different format as an additional command,
meillo@23 1023 instead of changing the default, he needs to create a link to
meillo@23 1024 \f(CWscan\fP, for instance titled \f(CWscan2\fP.
meillo@21 1025 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP,
meillo@45 1026 as the option should only be in effect for a program that is called as
meillo@21 1027 \f(CWscan2\fP.
meillo@20 1028
meillo@20 1029 .PP
meillo@33 1030 .B "Make every program a filter
meillo@21 1031 is hard to find in \s-1MH\s0.
meillo@21 1032 The reason therefore is that most of \s-1MH\s0's tools provide
meillo@45 1033 basic file system operations for mailboxes.
meillo@45 1034 It is the same reason because of which \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP,
meillo@45 1035 and \f(CWrm\fP aren't filters neither.
meillo@23 1036 \s-1MH\s0 does not provide many filters itself, but it is a basis
meillo@23 1037 to write filters for.
meillo@45 1038 An example would be a mail text highlighter,
meillo@30 1039 that means a program that makes use of a color terminal to display
meillo@30 1040 header lines, quotations, and signatures in distinct colors.
meillo@45 1041 The author's version of such a program is an awk script with 25 lines.
meillo@21 1042
meillo@21 1043 .PP
meillo@33 1044 .B "Build a prototype as soon as possible
meillo@21 1045 was again well followed by \s-1MH\s0.
meillo@21 1046 This tenet, of course, focuses on early development, which is
meillo@21 1047 long time ago for \s-1MH\s0.
meillo@21 1048 But without following this guideline at the very beginning,
meillo@23 1049 Bruce Borden may have not convinced the management of \s-1RAND\s0
meillo@23 1050 to ever create \s-1MH\s0.
meillo@23 1051 In Bruce' own words:
meillo@46 1052 .[ [
meillo@44 1053 ware rand history
meillo@46 1054 .], page 132]
meillo@21 1055 .QP
meillo@45 1056 [...] but [Stockton Gaines and Norm Shapiro] were not able
meillo@23 1057 to convince anyone that such a system would be fast enough to be usable.
meillo@21 1058 I proposed a very short project to prove the basic concepts,
meillo@21 1059 and my management agreed.
meillo@21 1060 Looking back, I realize that I had been very lucky with my first design.
meillo@21 1061 Without nearly enough design work,
meillo@21 1062 I built a working environment and some header files
meillo@21 1063 with key structures and wrote the first few \s-1MH\s0 commands:
meillo@21 1064 inc, show/next/prev, and comp.
meillo@21 1065 [...]
meillo@21 1066 With these three, I was able to convince people that the structure was viable.
meillo@21 1067 This took about three weeks.
meillo@0 1068
meillo@48 1069 .H 2 "Problems
meillo@0 1070 .LP
meillo@45 1071 \s-1MH\s0 is not without problems.
meillo@30 1072 There are two main problems: one is technical, the other is about human behavior.
meillo@22 1073 .PP
meillo@22 1074 \s-1MH\s0 is old and email today is very different to email in the time
meillo@22 1075 when \s-1MH\s0 was designed.
meillo@45 1076 \s-1MH\s0 adapted to the changes pretty well, but it is limited, though.
meillo@22 1077 \s-1MIME\s0 support and support for different character encodings
meillo@22 1078 is available, but only on a moderate level.
meillo@45 1079 This comes from limited development resources.
meillo@45 1080 More active developers could quickly change this.
meillo@45 1081 But \s-1MH\s0 is also limited by design, which is the larger problem.
meillo@22 1082 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend.
meillo@22 1083 These design conflicts are not easily solvable.
meillo@22 1084 Possibly, they require a redesign.
meillo@45 1085 \s-1IMAP\s0 may be too different to the classic mail model,
meillo@45 1086 which \s-1MH\s0 covers, so that \s-1MH\s0 may never support it well.
meillo@22 1087 .PP
meillo@45 1088 The other kind of problem are human habits.
meillo@45 1089 In this world, where almost all \s-1MUA\s0s are monolithic,
meillo@22 1090 it is very difficult to convince people to use a toolbox style \s-1MUA\s0
meillo@22 1091 like \s-1MH\s0.
meillo@45 1092 The habits are so strong, that even people who understand the concept
meillo@30 1093 and advantages of \s-1MH\s0 do not like to switch,
meillo@30 1094 simply because \s-1MH\s0 is different.
meillo@30 1095 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel,
meillo@45 1096 are quite outdated and thus not very appealing, compared to the modern interfaces
meillo@45 1097 of many monolithic \s-1MUA\s0s.
meillo@20 1098
meillo@48 1099 NH 2 "Summary \s-1MH\s0
meillo@20 1100 .LP
meillo@45 1101 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design.
meillo@31 1102 It consists of a toolchest of small tools, each of them does one job well.
meillo@31 1103 The toolchest approach offers great flexibility to the user.
meillo@45 1104 It is possible to utilize the complete power of the Unix shell with \s-1MH\s0.
meillo@31 1105 This makes \s-1MH\s0 a very powerful mail system.
meillo@45 1106 Extending and customizing \s-1MH\s0 is easy and encouraged.
meillo@31 1107 .PP
meillo@31 1108 Apart from the user's perspective, \s-1MH\s0 is development-friendly.
meillo@31 1109 Its overall design follows clear rules.
meillo@31 1110 The single tools do only one job, thus they are easy to understand,
meillo@31 1111 easy to write, and good to maintain.
meillo@31 1112 They are all independent and do not interfere with the others.
meillo@31 1113 Automated testing of their function is a straight forward task.
meillo@31 1114 .PP
meillo@31 1115 It is sad, that \s-1MH\s0's differentness is its largest problem,
meillo@31 1116 as its differentness is also its largest advantage.
meillo@31 1117 Unfortunately, for most people their habits are stronger
meillo@31 1118 than the attraction of the clear design and the power, \s-1MH\s0 offers.
meillo@0 1119
meillo@8 1120
meillo@8 1121
meillo@48 1122 .H 1 "Case study: uzbl
meillo@32 1123 .LP
meillo@32 1124 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0,
meillo@45 1125 which is an old and established software.
meillo@45 1126 This chapter covers uzbl, a fresh new project.
meillo@45 1127 Uzbl is a web browser that adheres to the Unix Philosophy.
meillo@45 1128 Its name comes from the \fILolspeak\fP word for ``usable'';
meillo@45 1129 it is pronounced identical.
meillo@0 1130
meillo@48 1131 .H 2 "Historical background
meillo@0 1132 .LP
meillo@32 1133 Uzbl was started by Dieter Plaetinck in April 2009.
meillo@44 1134 The idea was born in a thread in the Arch Linux Forums.
meillo@32 1135 .[
meillo@44 1136 arch linux forums
meillo@44 1137 browser
meillo@32 1138 .]
meillo@32 1139 After some discussion about failures of well known web browsers,
meillo@32 1140 Plaetinck (alias Dieter@be) came up with a very sketchy proposal
meillo@32 1141 of how a better web browser could look like.
meillo@32 1142 To the question of another member, if Plaetinck would write that program,
meillo@32 1143 because it would sound fantastic, Plaetinck replied:
meillo@32 1144 ``Maybe, if I find the time ;-)''.
meillo@32 1145 .PP
meillo@32 1146 Fortunately, he found the time.
meillo@32 1147 One day later, the first prototype was out.
meillo@32 1148 One week later, uzbl had an own website.
meillo@47 1149 .[
meillo@47 1150 uzbl website
meillo@47 1151 .]
meillo@32 1152 One month after the first code showed up,
meillo@47 1153 a mailing list was installed to coordinate and discuss further development,
meillo@47 1154 and a wiki was added to store documentation and scripts that showed up on the
meillo@32 1155 mailing list and elsewhere.
meillo@32 1156 .PP
meillo@45 1157 In the, now, one year of uzbl's existence, it was heavily developed on various branches.
meillo@32 1158 Plaetinck's task became more and more to only merge the best code from the
meillo@32 1159 different branches into his main branch, and to apply patches.
meillo@47 1160 .[
meillo@47 1161 lwn uzbl
meillo@47 1162 .]
meillo@32 1163 About once a month, Plaetinck released a new version.
meillo@32 1164 In September 2009, he presented several forks of uzbl.
meillo@47 1165 .[ [
meillo@47 1166 uzbl website
meillo@47 1167 .], news archive]
meillo@38 1168 Uzbl, actually, opened the field for a whole family of web browsers with similar shape.
meillo@32 1169 .PP
meillo@32 1170 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl.
meillo@47 1171 .[
meillo@47 1172 lwn uzbl
meillo@47 1173 .]
meillo@32 1174 In September 2009, the uzbl web browser was on \fISlashdot\fP.
meillo@47 1175 .[
meillo@47 1176 slashdot uzbl
meillo@47 1177 .]
meillo@0 1178
meillo@48 1179 .H 2 "Contrasts to other web browsers
meillo@0 1180 .LP
meillo@32 1181 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest,
meillo@32 1182 most web browsers are monolithic, but uzbl is a frontend to a toolchest.
meillo@32 1183 .PP
meillo@32 1184 Today, uzbl is divided into uzbl-core and uzbl-browser.
meillo@32 1185 Uzbl-core is, how its name already indicates, the core of uzbl.
meillo@32 1186 It handles commands and events to interface other programs,
meillo@45 1187 and also displays webpages by using \fIwebkit\fP as render engine.
meillo@32 1188 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar,
meillo@32 1189 an event manager, yanking, pasting, page searching, zooming, and more stuff,
meillo@32 1190 to form a ``complete'' web browser.
meillo@32 1191 In the following text, the term ``uzbl'' usually stands for uzbl-browser,
meillo@32 1192 so uzbl-core is included.
meillo@32 1193 .PP
meillo@32 1194 Unlike most other web browsers, uzbl is mainly the mediator between the
meillo@45 1195 various tools that cover single jobs.
meillo@35 1196 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket,
meillo@35 1197 and on stdin, and it writes events to a Unix socket and to stdout.
meillo@35 1198 Loading a webpage in a running uzbl instance requires only:
meillo@32 1199 .DS
meillo@32 1200 echo 'uri' >/path/to/uzbl-fifo
meillo@32 1201 .DE
meillo@45 1202 The graphical rendering of the webpage is done by webkit,
meillo@45 1203 a web content engine.
meillo@45 1204 Uzbl-core is built around libwebkit.
meillo@32 1205 .PP
meillo@45 1206 Downloads, browsing history, bookmarks, and the like are not provided
meillo@45 1207 by the core itself, like they are in other web browsers.
meillo@35 1208 Uzbl-browser also only provides, so called, handler scripts that wrap
meillo@35 1209 external applications which provide the actual functionality.
meillo@32 1210 For instance, \fIwget\fP is used to download files and uzbl-browser
meillo@32 1211 includes a script that calls wget with appropriate options in
meillo@32 1212 a prepared environment.
meillo@32 1213 .PP
meillo@32 1214 Modern web browsers are proud to have addons, plugins, and modules, instead.
meillo@32 1215 This is their effort to achieve similar goals.
meillo@35 1216 But instead of using existing, external programs, modern web browsers
meillo@45 1217 include these functions.
meillo@0 1218
meillo@48 1219 .H 2 "Discussion of the design
meillo@0 1220 .LP
meillo@32 1221 This section discusses uzbl in regard of the Unix Philosophy,
meillo@32 1222 as identified by Gancarz.
meillo@32 1223
meillo@32 1224 .PP
meillo@35 1225 .B "Make each program do one thing well" .
meillo@35 1226 Uzbl tries to be a web browser and nothing else.
meillo@36 1227 The common definition of a web browser is, of course, highly influenced by
meillo@36 1228 existing implementations of web browsers, although they are degenerated.
meillo@35 1229 Web browsers should be programs to browse the web, and nothing more.
meillo@45 1230 This is the one thing they should do.
meillo@36 1231 .PP
meillo@45 1232 Web browsers should not, for instance, manage downloads.
meillo@35 1233 This is the job download managers exist for.
meillo@35 1234 Download managers do primary care about being good in downloading files.
meillo@35 1235 Modern web browsers provide download management only as a secondary feature.
meillo@45 1236 How could they do this job better, than programs that exist only for
meillo@35 1237 this very job?
meillo@35 1238 And how could anyone want less than the best download manager available?
meillo@32 1239 .PP
meillo@35 1240 A web browser's job is to let the user browse the web.
meillo@35 1241 This means, navigating through websites by following links.
meillo@36 1242 Rendering the \s-1HTML\s0 sources is a different job, too.
meillo@36 1243 It is covered by the webkit render engine, in uzbl's case.
meillo@35 1244 Audio and video content and files like PostScript, \s-1PDF\s0, and the like,
meillo@36 1245 are also not the job of a web browser.
meillo@36 1246 They should be handled by external applications \(en
meillo@36 1247 ones which's job is to handle such data.
meillo@35 1248 Uzbl strives to do it this way.
meillo@36 1249 .PP
meillo@36 1250 Remember Doug McIlroy:
meillo@35 1251 .I
meillo@35 1252 ``Write programs that do one thing and do it well.
meillo@35 1253 Write programs to work together.''
meillo@35 1254 .R
meillo@35 1255 .PP
meillo@35 1256 The lesser tenet
meillo@35 1257 .B "allow the user to tailor the environment
meillo@35 1258 matches good here.
meillo@35 1259 There was the question, how anyone could want anything less than the
meillo@35 1260 best program for the job.
meillo@45 1261 But as personal preferences matter, it is probably more important to ask:
meillo@35 1262 How could anyone want something else than his preferred program for the job?
meillo@36 1263 .PP
meillo@45 1264 Usually users want one program for a specific job.
meillo@35 1265 Hence, whenever the task is, for instance, downloading,
meillo@45 1266 the same download manager should be used.
meillo@35 1267 More advanced users might want to have this download manager in this
meillo@35 1268 situation and that one in that situation.
meillo@35 1269 They should be able to configure it this way.
meillo@35 1270 With uzbl, one can use any download manager the user wants.
meillo@36 1271 To switch to a different one, only one line in a small handler script
meillo@35 1272 needs to be changed.
meillo@45 1273 Alternatively it would be possible to query the program to use by
meillo@45 1274 reading a global file or an environment variable, in the handler script.
meillo@36 1275 .PP
meillo@45 1276 Uzbl does neither have its own download manager nor depends on a
meillo@45 1277 specific one, hence uzbl's browsing abilities will not be lowered by having
meillo@35 1278 a bad download manager.
meillo@45 1279 Uzbl's download capabilities will be just as good as the ones of the best
meillo@36 1280 download manager available on the system.
meillo@38 1281 Of course, this applies to all of the other supplementary tools, too.
meillo@32 1282
meillo@32 1283 .PP
meillo@36 1284 .B "Use software leverage to your advantage" .
meillo@36 1285 Uzbl is designed to be extended by external tools.
meillo@36 1286 These external tools are usually wrapped by small handler shell scripts.
meillo@36 1287 Shell scripts are the glue in this approach.
meillo@36 1288 They make the various parts fit together.
meillo@36 1289 .PP
meillo@45 1290 The history mechanism of uzbl shall be presented as an example.
meillo@36 1291 Uzbl is configured to spawn a script to append an entry to the history
meillo@36 1292 whenever the event of a fully loaded page occurs.
meillo@45 1293 The script to append the entry to the history is not much more than:
meillo@36 1294 .DS
meillo@36 1295 #!/bin/sh
meillo@36 1296 file=/path/to/uzbl-history
meillo@36 1297 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file
meillo@36 1298 .DE
meillo@36 1299 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title.
meillo@45 1300 .PP
meillo@45 1301 For loading an entry, a key is bound to spawn a load-from-history script.
meillo@36 1302 The script reverses the history to have newer entries first,
meillo@45 1303 then displays \fIdmenu\fP to let the user select an item,
meillo@36 1304 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe.
meillo@45 1305 With error checking and corner case handling removed,
meillo@45 1306 the script looks like this:
meillo@36 1307 .DS
meillo@36 1308 #!/bin/sh
meillo@36 1309 file=/path/to/uzbl-history
meillo@36 1310 goto=`tac $file | dmenu | cut -d' ' -f 3`
meillo@36 1311 echo "uri $goto" > $4
meillo@36 1312 .DE
meillo@36 1313 \f(CW$4\fP expands to the path of the command input pipe of the current
meillo@36 1314 uzbl instance.
meillo@32 1315
meillo@32 1316 .PP
meillo@33 1317 .B "Avoid captive user interfaces" .
meillo@36 1318 One could say, that uzbl, to a large extend, actually \fIis\fP
meillo@36 1319 a captive user interface.
meillo@37 1320 But the difference to most other web browsers is, that uzbl is only
meillo@45 1321 the captive user interface frontend (and the core of the backend).
meillo@38 1322 Many parts of the backend are independent of uzbl.
meillo@45 1323 Some are distributed with uzbl, for some external programs,
meillo@45 1324 handler scripts are distributed,
meillo@45 1325 but arbitrary additional functionality can be added if desired.
meillo@37 1326 .PP
meillo@37 1327 The frontend is captive \(en that is true.
meillo@37 1328 This is okay for the task of browsing the web, as this task is only relevant
meillo@37 1329 for humans.
meillo@37 1330 Automated programs would \fIcrawl\fP the web.
meillo@37 1331 That means, they read the source directly.
meillo@37 1332 The source includes all the semantics.
meillo@37 1333 The graphical representation is just for humans to transfer the semantics
meillo@37 1334 more intuitively.
meillo@32 1335
meillo@32 1336 .PP
meillo@33 1337 .B "Make every program a filter" .
meillo@37 1338 Graphical web browsers are almost dead ends in the chain of information flow.
meillo@37 1339 Thus it is difficult to see what graphical web browsers should filter.
meillo@45 1340 Graphical web browsers exist almost only to be interactively used by humans.
meillo@37 1341 The only case when one might want to automate the rendering function is
meillo@37 1342 to generate images of rendered webpages.
meillo@37 1343
meillo@37 1344 .PP
meillo@37 1345 .B "Small is beautiful"
meillo@45 1346 is not easy to apply to a web browser, because modern web technology
meillo@45 1347 is very complex, hence the rendering task is very complex.
meillo@45 1348 Modern web browsers have to consist of many thousand lines of code,
meillo@37 1349 unfortunately.
meillo@37 1350 Using the toolchest approach and wrappers can split the browser into
meillo@37 1351 several small parts, tough.
meillo@37 1352 .PP
meillo@45 1353 As of March 2010, uzbl-core consists of about 3\,500 lines of C code.
meillo@37 1354 The distribution includes another 3\,500 lines of Shell and Python code,
meillo@37 1355 which are the handler scripts and plugins like a modal interface.
meillo@38 1356 Further more, uzbl uses functionality of external tools like
meillo@38 1357 \fIwget\fP and \fInetcat\fP.
meillo@37 1358 Up to this point, uzbl looks pretty neat and small.
meillo@38 1359 The ugly part of uzbl is the web content renderer, webkit.
meillo@37 1360 Webkit consists of roughly 400\,000 (!) lines of code.
meillo@38 1361 Unfortunately, small web render engines are not possible anymore
meillo@38 1362 because of the modern web.
meillo@35 1363
meillo@35 1364 .PP
meillo@35 1365 .B "Build a prototype as soon as possible" .
meillo@35 1366 Plaetinck made his code public, right from the beginning.
meillo@38 1367 Discussion and development was, and still is, open to everyone interested.
meillo@38 1368 Development versions of uzbl can be obtained very simply from the code
meillo@38 1369 repository.
meillo@38 1370 Within the first year of uzbl's existence, a new version was released
meillo@35 1371 more often than once a month.
meillo@38 1372 Different forks and branches arose.
meillo@45 1373 They introduced new features, which were tested for suitability
meillo@45 1374 for the main branch.
meillo@35 1375 The experiences of using prototypes influenced further development.
meillo@35 1376 Actually, all development was community driven.
meillo@38 1377 Plaetinck says, three months after uzbl's birth:
meillo@35 1378 ``Right now I hardly code anything myself for Uzbl.
meillo@35 1379 I just merge in other people's code, ponder a lot, and lead the discussions.''
meillo@35 1380 .[
meillo@44 1381 lwn
meillo@44 1382 uzbl
meillo@35 1383 .]
meillo@32 1384
meillo@0 1385
meillo@48 1386 .H 2 "Problems
meillo@0 1387 .LP
meillo@38 1388 Similar to \s-1MH\s0, uzbl, too suffers from being different.
meillo@38 1389 It is sad, but people use what they know.
meillo@38 1390 Fortunately, uzbl's user interface can look and feel very much the
meillo@38 1391 same as the one of the well known web browsers,
meillo@38 1392 hiding the internal differences.
meillo@38 1393 But uzbl has to provide this similar look and feel to be accepted
meillo@38 1394 as a ``normal'' browser by ``normal'' users.
meillo@37 1395 .PP
meillo@45 1396 Though, the more important problem is the modern web.
meillo@38 1397 The modern web is simply broken.
meillo@38 1398 It has state in a state-less protocol,
meillo@38 1399 it misuses technologies,
meillo@38 1400 and it is helplessly overloaded.
meillo@38 1401 The result are web content render engines that must consist
meillo@38 1402 of hundreds of thousands lines of code.
meillo@38 1403 They also must combine and integrate many different technologies,
meillo@45 1404 only to make our modern web accessible.
meillo@38 1405 Website to image converter are hardly possible to run without
meillo@38 1406 human interaction because of state in sessions, impossible
meillo@38 1407 deep-linking, and unautomatable technologies.
meillo@37 1408 .PP
meillo@38 1409 The web was misused to provide all kinds of imaginable wishes.
meillo@38 1410 Now web browsers, and eventually the users, suffer from it.
meillo@37 1411
meillo@8 1412
meillo@48 1413 .H 2 "Summary uzbl
meillo@32 1414 .LP
meillo@38 1415 ``Uzbl is a browser that adheres to the Unix Philosophy'',
meillo@38 1416 that is how uzbl is seen by its authors.
meillo@38 1417 Indeed, uzbl follows the Unix Philosophy in many ways.
meillo@38 1418 It consists of independent parts that work together,
meillo@45 1419 while its core is mainly a mediator which glues the parts together.
meillo@38 1420 .PP
meillo@38 1421 Software leverage can excellently be seen in uzbl.
meillo@45 1422 External tools are used, independent tasks are separated
meillo@45 1423 in independent parts and glued together with small handler scripts.
meillo@38 1424 .PP
meillo@38 1425 As uzbl, more or less, consists of a set of tools and a bit
meillo@38 1426 of glue, anyone can put the parts together and expand it
meillo@38 1427 in any desired way.
meillo@38 1428 Uzbl is very flexible and customizable.
meillo@38 1429 These properties make it valuable for advanced users,
meillo@38 1430 but may keep novice users from using it.
meillo@38 1431 .PP
meillo@45 1432 But uzbl's main problem is the modern web, that makes it hard
meillo@38 1433 to design a sane web browser.
meillo@38 1434 Despite this bad situation, uzbl does a fairly good job.
meillo@32 1435
meillo@8 1436
meillo@48 1437 .H 1 "Final thoughts
meillo@0 1438
meillo@48 1439 .H 2 "Quick summary
meillo@0 1440 .LP
meillo@0 1441 good design
meillo@0 1442 .LP
meillo@0 1443 unix phil
meillo@0 1444 .LP
meillo@0 1445 case studies
meillo@0 1446
meillo@48 1447 .H 2 "Why people should choose
meillo@0 1448 .LP
meillo@0 1449 Make the right choice!
meillo@0 1450
meillo@47 1451
meillo@47 1452 .bp
meillo@47 1453 .TL
meillo@47 1454 References
meillo@47 1455 .LP
meillo@47 1456 .XS
meillo@47 1457 .sp .5v
meillo@47 1458 .B
meillo@47 1459 References
meillo@47 1460 .XE
meillo@47 1461 .ev r
meillo@0 1462 .rm ]<
meillo@0 1463 .de ]<
meillo@0 1464 .LP
meillo@0 1465 .de FP
meillo@0 1466 .IP \\\\$1.
meillo@0 1467 \\..
meillo@0 1468 .rm FS FE
meillo@0 1469 ..
meillo@42 1470 .nr PS -1
meillo@42 1471 .nr VS -1
meillo@0 1472 .[
meillo@0 1473 $LIST$
meillo@0 1474 .]
meillo@47 1475 .nr PS +1
meillo@47 1476 .nr VS +1
meillo@47 1477 .ev
meillo@47 1478
meillo@42 1479 .bp
meillo@47 1480 .TL
meillo@47 1481 Table of Contents
meillo@47 1482 .LP
meillo@47 1483 .PX no